This invention relates to a stereocontrolled total synthesis of the known antibiotic thienamycin (I). ##STR2## The synthesis proceeds in a stereo-selective way via intermediate II: ##STR3## wherein R.sup.3 is a readily removable carboxyl protecting group, such as substituted and unsubstituted: lower alkyl, aryl and aralkyl, for example: methyl; ethyl; t-butyl; 1,1,1-trichloroethyl; benzyl; and phenyl.